A component of a security clearance and/or security class used for computing access rights and controlling information flow by restricting access to the information to a specific group of subjects. Note: [a] when more than one category is combined within a security class, access rights are granted only when all categories are present in the security clearance. [b] Adding a category to a security class restricts the group of subjects who may have access. [c] Codewords and Privacy and Restrictive markings may be represented by categories or caveats. See also: Caveat, Classification, Dominance [CESG].